This invention relates to an apparatus for sampling and analysis of thermally-labile species, such as mercury, arsenic, selenium, sulfur, lead, carbon, polyaromatic hydrocarbons, nxe2x80x94alkanes and the like, as may be associated with a variety of solid matrices (e.g., airborne particulate matter, suspended particles, soil materials, colloids). The invention also relates to a method of carrying out such sampling and analysis.
Various technologies exist for either collecting or separating particulate material from a fluid flow such as a gaseous stream. Such devices include filter packs which collect the material(s) of interest and the filter(s) then being treated as, for example, by using one or more acids or oxidation reagents, with the resulting final solution then being analyzed. In another example, a quartz wool stationary phase is used to retain particulate material on a manually-loaded plug contained in a quartz tube. The tube, along with the collected sample, are heated to an elevated temperature and the released elements of interest are detected and quantified. Yet another example is a miniaturized device using a quartz fiber filter disc. Particulate material, suspended in one or more gases or liquids, is trapped on the filter disc, following which the device is heated and the released elements detected and quantified.
When using filter packs, xe2x80x9cclean handsxe2x80x9d techniques and a clean-room facility are necessary for accurate results. Furthermore, ultra pure reagents, which are expensive, are required in those procedures involving sample treatment prior to analysis. This mode of operation is, therefore, time consuming and costly. Quartz wool plugs are difficult, if not impossible, to prepare uniformly. Hence, collection efficiency may vary from plug to plug. More importantly, sorption of gaseous species, for example elemental mercury vapor by the quartz wool, may generate erroneously high results in the determination of xe2x80x9cparticulate-phase mercuryxe2x80x9d in air. Miniaturized devices with a quartz fiber disc overcome the disadvantages of quartz wool plugs, but the filter disc becomes brittle after being heated at a high temperature, for example over 900xc2x0 C. A fresh filter disc is therefore required for each sample. Hence it is difficult to automate the whole measurement procedure, including sampling and sample analysis.
With prior art technologies, e.g. quartz wool plugs, it is a major problem to collect particles of sub-micron size in such a way that uniform and consistent sampling is obtained. It is a further problem to provide an efficient automated and economical procedure.
The present invention provides a novel apparatus, and a method, which is efficient, economical and which can be easily automated. In accordance with the present invention, there is provided a device for trapping particulate material in a fluid (usually/generally gaseous) stream, such as ambient air, or other fluid media, together with a pyrolyzer for sample pre-treatment prior to analysis. Thus, the present invention is suitable for sampling and analyzing mercury, for example, as well as other thermally-labile species. Broadly, a device of the present invention comprises a quartz housing with a filter member having a quartz bead plug and bead retainers such as quartz frits positioned on either side of the quartz beads. The housing, preferably in the form of a tube, is variable in length and in width. The porosity of the bead plugs may vary, as desired, depending on the size range of the particulate matter to be collected. The dimensions of the plug can vary as can the pore size of the quartz frits.
In the method in accordance with the inventions, a filter member comprising a quartz bead plug having quartz frits on either side thereof is loaded into a quartz housing e.g. a tube. A flow of fluid gas, for example air containing airborne particulate material, is passed through the tube with particulate material being collected in the quartz bead plug. After passage of the fluid, the whole unit may be positioned in a heating chamber where the tube and filter member are heated to a high temperature, for example up to 900xc2x0 C. or up to 1200xc2x0 C., for thermal desorption and subsequent analysis of the collected material by an analyzer located downstream of the sampling unit.